1. Field of the Invention
The present invention relates to an information processing system, such as a personal computer, and a control method therefor and in particular to an information processing system that has a power management function for reducing, as needed, the power supply to electric circuits that enter a low activity state, or for halting the power supply to them, and to a control method therefor. More specifically, the present invention pertains to an information processing system that provides both security (protection for secret data) and useability (operability) during a power saving operation, and to a control method therefor.
2. Description of the Related Art
As progress in the current technique continues, various types of personal computers (hereafter referred to as "PCS" or "systems"), such as desktop and notebook computers, are being manufactured and sold. The notebook PCS are being manufactured compact and light, since portability and outdoor use are taken into consideration. Almost all the notebook PCS, including those sold by IBM have "a structure with a cover" that comprises a body, which incorporates a system board and peripheral devices and has a keyboard on its top face, and a cover that has an LCD panel provided substantially at the center of the internal face. The cover is so hinged with the body at the rear edge as to be rotatable. A user opens the cover to use the PC and closes it when the PC is not in use or is to be carried.
One of the features of notebook PCS is that they are battery operated. Accordingly, they can be used at sites where there are no commercially available power sources. A battery that is used in a notebook PC is commonly formed as a "battery pack" which is a package that is comprised of a plurality of rechargeable battery cells, such as Ni-Cd, NiMH or Li-Ion. Although such a battery pack is reusable by being recharged, the charge capacity is sufficient to last only for two to three hours for the system operation time. Another feature of notebook PCS is that various ideas for power saving are taken to extend the duration of a battery pack.
Power saving in a PC can be realized not only by reducing the power consumption by the individual electric circuits, but also by halting, as needed, the power supply to electric circuits (or peripheral devices) that fall into low activity states. The latter method can be called "power management". The power management modes for the PC are modes which halt the power supply to individual devices, such as the back light of a Liquid Crystal Display (LCD) and a Hard Disk Drive (HDD) that account for the greatest share of the total power consumption by a full system. These modes are also called an "LCD back light-off" mode and an "HDD-off" mode respectively.
Another type of power management mode is a "Suspend" mode in which the power supply to all the electric circuits, except for a main memory, is halted. The power management is triggered by the expiration of a predetermined time (a time out value that is set for the suspend timer) since a last user input or a last system operation (e.g., a disk access of the HDD). The system may enter power management modes in response to an instruction by a user, such as the depression of a predetermined function key (a suspend key). In a power management mode, such as the suspend mode, when key/mouse input is again effected by a user, or when a system operation is restarted, the power supply is resumed and a suspended task is begun again at a point just before the transition to the power management mode. For example, ThinkPads 700/750/755 (a trademark of IBM Corp.) that are sold by IBM have a suspend function.
At present, from an ecological view point, the demand for power management is increasing, even for desktop PCS to which power can be supplied almost unlimitedly by commercially available power sources. In June 1993, the U.S. Environmental Protection Agency (EPA) advocated a self-control action that is called the "Energy Star Computer Program", and required that consumed power in the standby state be a predetermined value or lower (drive power is to be less than 30 W, or 30% or less than that when the CPU is active). Computer makers have developed and manufactured products that conform to the advocated action. For example, PS/55E (for which "Green PC" is a common name) that is sold by IBM has a suspend function. The IBM PC 750 and Aptiva (a trademark of IBM Corp.) series incorporate a FAX function, and also have a rapid resume function, which correspond to hibernation for the purpose of saving power consumption during the course of the standby state until receiving data.
On the other hand, as the times have been changing, security in the office has become important. Various locking mechanisms have been proposed and implemented into products in order to protect PC bodies and expensive expansion devices (e.g., HDD packages and PC cards) from being stolen. A mechanism for inhibiting the removal of an HDD is disclosed in, for example, Japanese Patent Application No. Hei 04-246292 (Japanese Unexamined Patent Publication No. Hei 06-119082: Our company reference No. JA9-92-030), which was assigned to the present applicant. A mechanism for inhibiting the removal of a PC card from a PC card slot is disclosed in, for example, Japanese Patent Application No. Hei 05-182972 (Japanese Unexamined Patent Publication No. Hei 07-44269: Our company reference No. JA9-93-030).
As for security, not only physical theft but also theft at the software level such as the invasion (data access) of a system by an unauthorized user must be taken into consideration. To maintain security while an authorized user is absent from the system there is a computer of the type that prompts a user to input a password when the system is powered on (during the course of executing a power on self test (POST) program). When a user is absent from the front of the PC, the system is not only being powered down but also falls into a power management mode such as the suspend mode. It is because a predetermined time, that may be set by the suspend timer, will sometimes elapse while a user is absent from the front of the PC. Therefore, the number of computers have increased that prompt a user to input a password (also called a "resume password", which may be the same password as that of power-on password) even when resuming from the suspend mode. Many of the recent PCS sold by IBM have a resume password function.
"Suspend" more specifically means a function for halting the power supply to all the electric circuits, except for a main memory in which are stored data (hardware context data, such as the I/O setup state, the status of a CPU and the contents of a VRAM) that are required for the resumption of a task. The recovery operation from the suspend mode is performed substantially in an inverse sequence by restarting the power supply to the individual electric circuits and restoring the saved data to its original locations. As a result, a suspended task can be begun at a point just before the mode transition. The recovery from the suspend mode is called "Resume". A trigger for entering the suspend mode may be the selection of a suspend icon (by double clicking on it), the closing of the cover (the LCD panel) of a notebook PC, or some other operation, in addition to the depression of a suspend key (previously described).
It is obvious that, as the time out value of the suspend timer is determined to be shorter, the effect of the power saving is increased because the system enters the suspend mode earlier. Once the system enters the suspend mode, the system prompts a user to input a password. The password prompt function may be necessary for protecting the security of the system. However, such password input operation may sometimes be troublesome for a user.
When the transition to the suspend mode has occurred upon the request by a user (for example, depression of a suspend key), it can be assumed that the user agrees with the password input operation in recovering from the suspend mode. However, in a case where the mode transition is caused by the suspend timer, the password input operation may be irritating to the user. It is because the system enters the suspend mode while the user is simply relaxing and resting from a job (or when the user is thinking, has halted data input operations by being engaged in a sudden telephone conversation, or is talking to another person while sitting in front of the PC). When a system enters the suspend mode against a user's will, he tends to request to resume from the suspend mode because he is irritated by the mode transition. And when immediately thereafter the user is confronted with a demand that a password shall be entered, the user becomes even more exasperated. In other words, the useability of the PC is deteriorated. The easiest method to resolve the problem of useability is to obviate the password input operation when resuming from the suspend mode. It takes about 5 seconds to restore the data that was stored in the main memory to the original locations. So, if a password input operation is eliminated, the resuming operation can be completed in a moment and the task can be instantaneously recovered. It is, however, improbable that the requirement for the input of a password will be removed under the present conditions where the need for improved system security is constantly stressed. The irritation that a user feels when the system suddenly enters the suspend mode and is then prompted to input a password may be eliminated by setting the time out value of the suspend timer to be a relatively greater value. It is because the system under the greater time out value never enters the suspend mode unless it is surely presumed that a user has removed from the PC. However, in such a case, the power saving effect is considerably reduced because the system enters the suspend mode after a long period of inactivity. That is, in order to obtain a greater power management effect for a PC, a trade-off between useability and security is sometimes required.